Locator system for implanted access port with RFID tag

ABSTRACT

An access port locator system for adjustable gastric bands. The system includes an access port with an RFID tag with its antenna adjacent to the receiving portion of the port. The system includes a locator with radio frequency transmitter/receiver circuitry for sending read or interrogation signals to the RFID tag and for sending write signals to the tag to write treatment data to memory of the RFID tag. The locator also includes an antenna array with four patch antenna arranged in pairs to model two monopulse radar antenna systems. The locator also includes processor(s) and logic modules/circuitry for processing the tag response signals received by the antenna array to determine location information for the RFID tag and associated port, i.e., to identify the center of the port relative to the antennae array or array face such as with strength and direction information relative to the array face.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to devices and methods forcontrolling obesity, and, more particularly, a system and method foraccurately locating a port of an inflation/deflation tube for animplanted gastric band to allow a needle to be inserted into the centerof the port. The present invention also relates to the use of radiofrequency identification (RFID) technology for reading and writing datato an implanted medical device (IMD) such as a gastric bandinflation/deflation port.

2. Relevant Background

Severe obesity is an increasingly prevalent chronic condition that isdifficult for physicians to treat in their patients through diet andexercise alone. Generally, gastrointestinal surgery promotes weight lossby restricting food intake, and more specifically, restrictiveoperations limit food intake by creating a narrow passage or “stoma”from the upper part of the stomach into the larger lower part, whichreduces the amount of food the stomach can hold and slows the passage offood through the stomach. Initially, the stoma was of a fixed size, butphysicians have more recently determined that the procedure is moreeffective if the stoma can be adjusted to alter its size. One of themore commonly used of these purely restrictive operations for obesity isadjustable gastric banding (AGB).

In an exemplary AGB procedure, a hollow band (i.e., a gastric band) madeof silicone elastomer is placed around the stomach near its upper end,creating a small pouch and a narrow passage (i.e., a stoma) into therest of the stomach. The band is then inflated with a saline solution byusing a non-coring needle and syringe to access a small port that isplaced under the skin. To control the size of the stoma, the gastricband can be tightened or loosened over time by the physician or anothertechnician extracorporeally by increasing or decreasing the amount ofsaline solution in the band via the access port to change the size ofthe passage or stoma.

After a port has been placed in a patient, it is often difficult tolocate the port, and to support insertion of a needle, the center of theport needs to be located for the technician or physician who isinjecting or withdrawing saline. The location process is complicated asthe port is typically positioned beneath the patient's skin andsometimes beneath other tissue such as fat. Presently, port location isaccomplished through the use x-rays and or fluoroscopes. However, thesetechnologies are expensive to use, require an additional technician tooperate the location equipment, and may require the port to bemanufactured with materials that are more suited for locating but thatare less biocompatible. As a result, the medical industry continues todemand a less complex and costly devices and methods for locating theinflation/deflation port for adjustable gastric band systems whilerequiring that the port locating devices be accurate and relatively easyto use.

Additionally, with implantable medical devices (IMDs), it is oftendesirable to be able to read data from the IMD and, in some cases, towrite data to the IMD. For example, medical device developers havecreated IMDs that include passively powered radio frequency (RF)transponders and these transponders are powered to communicate with anexternal transmitter/receiver. The passive RF device has programmablememory for storing information related to the device and/or the patient.For example, the information may include patient demographics, implantdata, and manufacturer or device information (e.g., manufacturer ID, IMDmodel, serial numbers, and the like). In other cases, sensors areprovided with the IMD to obtain patient information such as bloodpressure, and the sensor collected data is transmitted from the IMD toan external transmitter/receiver device.

Some of these RF-based devices require the transmitter/receiver to beheld within a relatively close distance of the implanted device toobtain accurate signals from the IMD, and efforts have been made bydevelopers to measure the quality of the RF signals received from thetransponder on the IMD to determine when the transmitter/receiver iswithin an acceptable range of the IMD transponder and an audio signalmay be used to indicate an acceptable relative distance between the twodevices. However, the determination that an IMD and atransmitter/receiver are within a particular distance from each other isnot particularly useful for inserting a needle into a center of agastric band port where the accuracy required is measured inmillimeters.

Hence, there remains a need for an improved method and system forlocating a center of an inflation/deflation or “access” port of agastric band after it has been implanted within a patient or forlocating other implanted IMD accurately. Preferably, such a method andsystem would provide effective feedback to a technician or physicianattempting to insert a needle within the center of the access port so asto facilitate accurate insertion of the needle. Further, it ispreferable that such a method and system be compatible with reading datafrom the access port (or other IMD) and, in some cases, for writing datato the access port (or other IMD).

SUMMARY OF THE INVENTION

The present invention addresses the above and other problems byproviding a port locator system and method for use in gastric bandsystems for accurately locating the access port for an inflate/deflateline to allow an operator to adjust the size of a stoma on a periodicbasis. The port locator system includes an RFID-enabled access port,i.e., an access port with an RFID tag mounted on it with the antenna ofthe tag being positioned such that response signals indicate the centerof the port (or a face used to receive needles), which can be achievedby coiling the antenna along the wall of the port (or about theperiphery of the receiving surface). The port locator system alsoincludes a locator with RF transmitter/receiver circuitry for sendingread or interrogation signals to the RFID tag and for sending, in someembodiments, write signals to the tag to write patient treatment data(such as patient information and adjustment information for the band) tomemory of the RFID tag. The locator also includes an antenna array thatin some cases includes four patch antenna arranged in pairs to model twomonopulse radar antenna systems. The locator also includes processor(s)and logic modules/circuitry for processing the tag response signalsreceived by the antenna array to determine location information for theRFID tag and associated port, i.e., to identify the center of the portrelative to the antennae array (or array face) such as with strength anddirection information relative to the array face.

More particularly, a gastric band system is provided that is adapted forlocating an access port with radio frequency technology. The systemincludes a gastric band with a fill line having an access port forreceiving a needle and that has an RFID tag. A locator is provided inthe system for locating the access port. The locator includes a radiofrequency transmitter that generates a read or interrogation signal,which the RFID tag on the port responds to by generating a tag responsesignal. The locator also includes an antenna array that is used by theRF transmitter to transmit the interrogation signal and is alsofunctions to receive the tag response signal from the RFID tag. Thelocator uses a location processing module to process the tag responsesignal to determine location information for the access port, which mayinclude strength information and direction information relative to anantenna array face and which may be displayed via a GUI or other userinterface on a display element of the locator.

The access port may include a surface for receiving the needle and theRFID tag typically includes an antenna (such as a coil antenna) that ispositioned about the periphery of the receiving surface of the port(such as on a port wall defining the receiving surface) such that thelocation information determined for the access port is indicative of thecenter of the receiving surface. The antenna array may be made up of twopairs of antennae that are positioned an equal distance from each other(within the pair and from adjacent ones of the antennae) and anpredetermined distance from a central axis of the antenna array (i.e., aline passing through a point in the plane containing the antenna pairsthat is substantially in the center of the antennae). The locationprocessing module preferably functions to process difference signals foreach of these pairs of antennae to determine the location informationfor the access port, with the difference signals being generated in theantenna array based upon the tag response signal as received by each ofthe antennae. The locator may include a receiver processing module thatoperates prior to the location processing module to generate an in-phasetag response signal and a quadrature tag response signal from each ofthe difference signals. The locator may also include a tag dataprocessing module that processes a sum signal generated by the antennaarray based on the tag response signal to obtain tag data stored inmemory of the RFID tag, whereby the locator is able to read data on theRFID tag. Further, the RF transmitter of the locator may be operated togenerate a write signal, e.g., based on operator input entered via akeypad or other I/O component of the locator, that is transmitted to theRFID tag via the antenna array, with the RFID tag operating in responseto store data in the write signal to persistent tag memory, whereby thelocator is operable to write patient treatment data to the access port.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an adjustable gastric band system with an RFID portlocator system according to the present invention as it may be used intreating a patient;

FIG. 2 is a block diagram of a port locator system of the invention,such as may be used in the gastric band system of FIG. 1 to locate thean implanted access port;

FIG. 3 illustrates generally the monopulse antenna concept that isincorporated in the use of paired antennae in the antenna system ofembodiments of the invention;

FIG. 4 is a view of the antenna system of one embodiment of theinvention with a portion of the locator housing removed to show twopairs of patch antennae with a recessed surface for receiving asyringe/needle centered between the antennae;

FIG. 5 is a functional block diagram of an embodiment of the antennasystem provided in a locator of the present invention;

FIG. 6 is a schematic and/or functional block diagram of an embodimentof a receiver processing module provided in a locater of the presentinvention;

FIG. 7 is a schematic and/or functional block diagram of an embodimentof a location processing module provided in locators of the presentinvention; and

FIG. 8 is a schematic and/or functional block diagram of an embodimentof a tag data interpretation/programming logic module provided in portlocators of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In brief, the invention is directed to a gastric band system with anaccess port locating functionality that enables an operator (e.g., aphysician or technician) to accurately locate an access port of a filltube (or inflation/deflation line) for a gastric band after implantationin a patient. The invention may also be said to be directed to a portlocator method and system for use with adjustable gastric bands. Theport locator method is useful for locating an access or inflation portto a degree of accuracy which allows a doctor or technician to insert aneedle into the center of the access port. To this end, the access portof the gastric band system is RFID-enabled and a locator is operated tocommunicate with the RFID-enabled or tagged port, which may includeread-only or read/write memory for storing information related to theport/band and/or the patient. The term “locator” is used herein todescribe technology and components that may include or build uponstandard RFID “readers” or “interrogators” (e.g., the locator may beconsidered an enhanced/modified RFID reader or interrogator).

The locator may be a handheld device that includes a microprocessor,memory, a specially configured antenna array or system, andlogic/circuitry that function in conjunction to determine precisely thelocation of the port based on RF signals transmitted from the port andto display the location information to an operator via a display and agraphical user interface. The handheld locator typically is also adaptedwith a receptacle for holding a syringe and needle so facilitateinsertion of the needle in the center of the port base on displayedlocation information. Further, the locator is operable to read data fromthe port's RFID tag memory that is displayed to the operator on thedisplay and, optionally, is operable to write data to the port's RFIDtag memory for long term storage that can later be read by the locatoror other RFID devices. For example, this data or information may includeband or port serial number, size and/or type of band, patientinformation and/or demographics, adjustment volumes, and adjustmentdates/times, which allows the device, patient, and adjustment ortreatment history to be stored on or at the access port of the gastricband. The access port location features of the invention can be usedwith numerous gastric band designs and are particularly useful for thosethat include an inflatable portion, e.g., an inner lumen, that isexpanded or contracted by increasing or decreasing the volume of fluidcontained therein via an access port (or inflation/deflation port).

FIG. 1 illustrates a gastric band system or apparatus 100 as it mayappear when installed in a patient being treated for morbid obesity. Asshown, the system 100 is being used to form a stoma or smaller openingin the upper portion of the stomach near the esophagus to restrict foodintake and flow. It is often useful or even necessary to vary the sizeof the stoma to properly treat a patient, e.g., to initially set a sizeof the stoma and then, later alter its size by adding or withdrawingfluid via port 120. Hence, the gastric band system 100 is adapted foradjustment of its size. The gastric band system 100 includes a gastricband 110 that is inflatable by external or extracorporeal actions via afill tube or line 112 that is connected to an access port 120 throughwhich fluid can be pumped into the inflatable portion or member of thegastric band 110. Such a filling if typically performed as part of aninitial sizing of the stoma as part of the implanting process performedby the physician or other technician and at later treatment sessions. Toperform such filling (and withdrawing) of the band 110, the physician ortechnician needs to be able to accurately locate the access port 120even though it may be beneath skin and other tissue.

The band 110 and other components of the system 100 are implanted in thesame or similar surgical procedure as used with existing expandable orinflatable gastric bands. For example, a surgeon would typically dissectthe tissues around the stomach to create a tunnel for the band 110. Theband 110 is then introduced into the patient's abdomen, e.g., through an18 mm or other sized trocar or the like or directly through the trocarhole in the skin. The band 110 is then tunneled in place and positionedaround the stomach. The other components of the system 100 are placednear the stomach (such as just below the skin on top of the sternum oron the rectus muscle sheath proximate the access port) with fluidconnection provided via port 120 and fill/drain line 112 to the gastricband 110 and particularly to the inflatable or expandable member orportion of the band 110.

The access port 120 of the gastric band system 100 includes a wall 122extending away from the tube 112 to a face or surface 124 that has asealable or self-sealing opening with a center 126, e.g., the port 120is formed to receive a needle (such as needle 161) but to seal when theneedle is withdrawn to block flow of fluid out of the tube 112. Toinflate or deflate the band 110 to adjust the stoma, an operator of thesystem 100 locates the port 120 with such accuracy that the face orsurface 124 and the port center 126 can be identified and a needle (suchas needle 161) guided into the port 120 at the center 126.

To this end, the port 120 is “RFID-enabled” by the inclusion of an RFIDtag 128 that is mounted on the wall 122 of the port 120. The antenna 129of the tag 128 preferably is positioned to extend about the periphery orcircumference of the generally circular face or surface 122 such as bybeing mounted on the port wall 122. In this manner, the signals 162transmitted from the RFID tag 128 in response to interrogation signalsfrom a locator 150 facilitate location or identification of the center126 of the surface or face 124 of the port 120. Alternatively, theantenna 129 may be mounted within the tag 128 and the antenna's locationor offset relative to the center 126 may be measured/predetermined andutilized in the location processing modules or logic of the locator 150to determine the location of the center 126 based on the signals 162.

The system 100 further includes a locator 150 that includes a displayelement 154 that is used to display data read from the port tag 128 viawireless or RF communications 162 with the RFID tag 128 and antenna 129,to display data such as adjustment or patient information to be writtento memory of the RFID tag 128, and, significantly, to display locationinformation or information useful for positioning the handheld locator150 relative to the center 126 of port 120. The locator device 150 alsoincludes a keypad or other input area 156 for allowing an operator toenter data or input to be written to the RFID tag 128 or to query forread data or the location of port 120. The locating method performed bythe locator 150 is discussed in detail below with reference to FIGS.2-8.

The locator 150 as shown may include a recessed surface or receptacle158 in its housing 152 for receiving a syringe 160 with a needle 161.This may be useful for facilitating positioning of the needle 161 on thecenter 126 of the port face 124 while viewing the location informationon the display 154. The receptacle 158 preferably would include achannel or hole that allows the needle 161 to extend through the locator150 for insertion into the port 120 when the locator housing 152 isproperly positioned relative to the port 120 as indicated on the display154. In some embodiments, the receptacle 158 is positioned in thehousing 152 such that the needle 161 of the syringe 160 extendstransverse (and often perpendicularly) to a board or mounting plate(e.g., a planar element) on which the antenna system is mounted, andmore specifically, so as to extend through the center of antennae insuch an antenna system (as is explained in more detail below). Such apositioning allows ready translation of the determined location of theport 120 to the relative position of the handheld locator 150. Ofcourse, the syringe 160 may be mounted on the housing 152 in a differentmanner (or even provided separately) with the relative position of theneedle 161 of the syringe to the antenna system being taken into accountto assist an operator in inserting the needle 161 into the center 126 ofthe port face 124.

The gastric band 110 may take many forms to practice the invention. Forexample, but not as a limitation, the gastric band 110 may be configuredsimilar to the gastric bands described in U.S. Pat. Nos. 5,226,429 and5,601,604, which are incorporated herein in their entirety by reference.Alternatively, the gastric band 110 may include one of the gastric bandsavailable from Inamed Corporation (e.g., one of the bands in theLAP-BAND™ family of expandable gastric bands such as the 9.75, 10.0,11.0 cm, the VG, or AP LAP-BANDs). Other gastric bands from various bandmanufacturers/distributors that could be used for this applicationinclude, but are not limited to: the Obtech (Ethicon) band, the AMIband, the Heliogast band, the Minimizer (Pier) band, and Cousin Bioband.

FIG. 2 illustrates in block form a port locator system 200 such as maybe used within a gastric band system (e.g., system 100 of FIG. 1). Asshown, the port locator system 200 includes a locator 210 thatcommunicates read/write data via RF or wireless signals 260 with an RFIDtag 280 that is mounted on or provided as an integral part of an accessport 270 for a gastric band (not shown). The locator 210 is typically ahandheld device and includes a controller/microprocessor 212 thatmanages operation of components and logic on the locator 210. Thefunctionality of the locator 210 as described herein (and with referenceto FIGS. 3-8) may be implemented with software or logic and/or withappropriate hardware/circuitry components. The locator 210 includesmemory (RAM and/or ROM), a power supply 216 such as a rechargeablebattery or the like, a display 218 such as an liquid crystal display(LCD) or the like, a keypad and/or other input device 220, and a userinterface 222 (such as a GUI for use in displaying location of the port270 relative to the locator 210 on the display 218).

The locator 210 functions to communicate with the RFID tag 280 and inthis regard, the locator 210 includes an RF transmitter/receiver 230with an antenna system 234 and a receiver processing module 238 (each ofwhich is described further below). The locator 210 further includes alocation processing module 240 for determining the location of the port270 relative to the locator 210 and more specifically, relative to theantenna system 234. A tag data processing module 250 is provided forprocessing data read from the tag 280 and for use in displaying the dataon display 218 via user interface 222 and for facilitating writeoperations to the tag 280.

The RFID tag 280 is provided on the port 270 so as to RFID enable theport and allow it to be located by the locator 210. The RFID tag 280includes at least telemetry circuitry/antenna 282 and memory 284 forstoring tag data 286, such as serial number, band type and size, and thelike, and patient data 288, such as adjustment or treatment informationand demographic information. The RFID tag 280 may take various forms topractice the invention. Typically, in a read/location operation of thesystem 200, the RF transmitter/receiver 230 (or “reader”) initiatescollection of data 286, 288 by sending a message 260 to the tag 280. TheRFID tag 280 is typically an inductively coupled RFID tag with thecircuitry 282 being powered by the magnetic field generated 260 by theRF transmitter/receiver 230 as the antenna picks up the magnetic energyand, then, the tag 280 communicates via signals 260 with the receiver230 of locator 210 via antenna system 234. The telemetrycircuitry/antenna 282 may include a silicon microprocessor or chip and ametal coil or other type of antenna (such as conductive carbon ink orthe like). In other embodiments, the RFID tag 280 is an active tagpowered by a battery (not shown) or is a passive tag that iscapacitively coupled for powering by the locator 210 (rather than beingpassive and powered inductively by the locator 210).

During operation, the tag 280 responds to the locator 210 via signals260 when it is within the locator's field, i.e., the tag 280 has a rangethat is typically selected to be relatively short such as less thanabout 20 feet and more typically very short such as less than about 2feet or the like. The frequency range may also vary significantly topractice the invention and in some short range applications, thefrequency utilized may be a low frequency such as one selected in therange of 30 KHz to 600 KHz or higher. The RFID tag 280 is preferablyselected to have relatively good propagation, i.e., a good ability toperform tag-locator communication through objects and material such ashuman tissue. The antenna 282 in the tag 280 may be selected to havedirectional coverage (rather than being omni-directional) to provide RFcoverage that is stronger in a specific direction such as in thedirection perpendicular to the face of the port to facilitateidentification of the center of the port 270. The memory 284 may be readonly, read/write, or even write once/read many and may vary in size suchas 16 bits to 512 kBytes or larger.

According to the invention, port location is accomplished by processingsignals from an RFID tag provided with an access port of a gastric band.To this end, antenna systems of the invention (such as those in locator150 of FIG. 1 and antenna system 234 of FIG. 2) are modeled after amonopulse radar antenna system 300 shown conceptually in FIG. 3. In theantenna system 300, a pair of antennae such as patch antenna operates toform a sum beam pattern 330 that maximizes directly over the antennasystem face. Also, the monopulse radar antenna system 300 operates toform a delta beam pattern that appears as two adjacent lobes 310, 320and that has a null response directly over the antenna system face. Thebehavior of the modeled system 300 can be used and expanded upon toenable detection of the location of a transmitting device, such as anRFID tag or its antenna provided on an access port.

The locator system of the invention can be thought of as containingthree component parts: an antenna system with RF beam forming components(e.g., antenna system 234 of FIG. 2), an analog receiver processingmodule (e.g., element 238 of FIG. 2), and a digital signaldetection/control interface component (e.g., elements 240 and 250 ofFIG. 2). Each of these components is described in the followingdiscussion with reference to FIGS. 4-8.

FIG. 4 illustrates one useful embodiment of an antenna system 400 foruse in locators of the present invention. As shown, the antenna system400 is provided as a two-dimensional (2-D) array of paired antennae 420and 430 and paired antennae 440 and 450. The antennae 420-450 may bepatch antenna or some other useful form of antenna for communicatingwith an RFID tag, and the paired antennae 420-450 are mounted on aplanar base, board, or plate 410. More specifically, the antennae420-450 are arranged to form two monopulse radar antenna systems such asshown in FIG. 3. The two pairs of antennae 420, 430 and 440, 450 arearranged to form a diamond shape with an up/down set 440, 450 and aleft/right set 420, 430. The antennae 420-450 are spaced equidistantlyfrom each other and about a center that is marked with dashed lines inFIG. 4. In embodiments in which the syringe is received and directedthrough the locator housing, the antennae mounting element or plate 410includes a recessed surface 424 in the center of the antenna systemformed by antennae 420-450 and a hole or channel 418 that extendsthrough the plate 410 is provide to allow a needle to pass through theplate 410.

FIG. 5 illustrates an antenna system 500 in block form to betterillustrate circuitry useful in implanting a locator device to locateaccess ports. As shown, the system 500 includes a left patch 510 that ispaired with a right patch 512 and an upper patch 514 that is paired witha lower patch 518 (and that may be arranged physically as shown in FIG.4). One pair, formed by two of the opposing antennae such as the leftand right patch antennae 510, 512, is fed with a signal divider circuit520 that provides the sum 526 of the two antenna signals to a powerdivider 540 as well as outputting the difference 522 to the receiverprocessing module. Similarly, the other pair, formed by the otherorthogonal pair such as the upper and lower patch antennae 514, 518, isfed with a signal divider circuit 530 that provides the sum 536 to thepower divider 540 as well as outputting the difference to the receiverprocessing module. Both feeds are bi-direction, e.g., the feeds to theantennae perform the same signal manipulation for signals radiating fromthe antenna elements 510-518 as for signals being received by theantenna elements 510-518 (i.e., emanating from the RFID tag).

The sum signals 526, 536 from each feed network (U/D and L/R pairs) arecombined and processed through a receiver processing module (as shown inFIG. 6). The difference signals 522, 532 (one from each antenna pair)are also routed to a set of receiver modules. The end result for the sumpath is to create a single beam at the array face. This single beam atthe array face for the locator antenna system allows the locator toread/write an RFID tag on a port much the same as normal antenna wouldallow a standard RFID tag reader to operate but while enabling thedetermination of the location of the tag and its corresponding port. Forexample, in a test system fabricated by the inventor, the sum path wasconnected to a standard reader with good results.

The difference signals 522, 532 are processed to obtain locationinformation for the port based on signals received from the RFID tagantenna. The array is mechanically modified in some embodiments toprovide a physical way of accommodating an inflate/deflate syringe orneedle so as to keep the needle substantially perpendicular to theantenna array face, which aligns the needle with the delta pattern (U/Dpair and L/R pair) nulls. For example, the array may be arranged asshown in the system 400 of FIG. 4.

Locator devices typically include a receiver processing module (such asmodule 238 of the RF transmitter/receiver 230 of FIG. 2). As shown inFIG. 6, a receiver processing module 600 is provided for receiving thesum and difference signals from the antenna system. The receiverprocessing module 600 functions to complete the analog processing forall three antenna system outputs 604 that are fast fed to an inputsignal divider that outputs to RF ports 622, 632 of a pair of mixers620, 630. The mixers 620, 630 mix the received high frequency signalwith the transmitted signal provided on an LO port 626, 636 from areference component 640 that utilizes a transmitted signal sample 646 togenerate the reference transmitted signal to the mixers 620, 630. Bymixing the received signal from the port tag with the transmittedsignal, the processing module 600 translates any high frequency tagresponse signals down to DC.

Filters 650, 660 are provided on the IF ports 624, 634 to follow thesignal conversion to separate the port tag's response further from thetransmitted signal and, also, from background reflections and to outputan in-phase tag response signal at 658 and a quadrature tag responsesignal 668. In this regard, the filters 650, 660 may be 2-stage bandpassfilters. This is possible due to the manner in which the tag impartsinformation onto the signal that is transmitted to it. Namely, the tagcreates a periodic interference at its data rage (e.g., at approximately32 kHz in some embodiments). It is this frequency-separated tag signalthat is used by the reader (or other components of the locator) to readback information from the tag and, significantly for the presentinvention, for providing direction and/or location. Since the 2-Dantenna array provides two difference signals, i.e., one from eachdimension (from the L/R pair of antennae and from the U/D antennaepair), moving the antenna array face until both of these differencesignals are minimized provides an accurate indication of the location ofthe RFID tag and, directly or indirectly depending on the access portconfiguration, the center of the corresponding port face or surface.

FIG. 7 illustrates a block diagram of a location processing module 700(such as may be used for module 240 of the locator 210 of FIG. 2). Themodule 700 takes as input the in-phase tag response signals 702, 706from the antenna pairs at A/D converters 710, 714. The module 700 alsotakes as input the quadrature tag response signals 704, 708 from theseantenna pairs at A/D converters 712, 718. The module 700 processes theseL/R and U/D difference signals 702-708 to provide direction and strengthinformation for determining location information for the port (e.g., forlocating the port having the responding RFID tag). To this end, themodule 700 also takes as input a transmit timing synchronization signal709 (e.g., from the RF transmitter/receiver or controller based on atime of transmitting the interrogation signal from the locator to theRFID tag).

Although other software modules/circuitry may be used, the locationprocessing module 700 is shown to process the response signals withzero-crossing and phase detection logic 720, 724 and with absolutemagnitude computation logic 730, 736 with the output of these logicelements being provided to the position, steer, and null components 740,748 with the transmit timing synchronizations signal 709. Thecomputational modules 740, 748 provide their output to position display750, which may be run as a separate component or as part of the userinterface of the locator by the controller/processor to provide on adisplay location information that can be used by operator to positionthe locator or, more precisely, the antenna array or system in thelocator such that the array face is perpendicular and directly above thecenter of the port. For example, a visual representation of the locationinformation may be generated by the position display 750 or othercomponents on the display of the locator that provides direction andstrength portions of the port location information that should “steer”or direct the operator to move the array face (the locator) directlyover and perpendicular to the port (i.e., over the tag). Theinflate/deflate needle can then be inserted directly into the center ofthe port face.

Output from the processing module will be used to direct the user by theuser interface on the external control device. An example of the userinterface could be a circular array of arrows that light up or changecolor to direct the user. This user interface could be accomplished withan LCD screen or an array of LED lights. The output will identify arelative distance and direction in which the user needs to move thecontroller to be over the center of the internal tag and antenna. Forexample, when the user is 3 to 4 inches southeast of the port center,the controller may register and one light in the northwest quadrant ofthe circular array may light up indicating the user should move thecontroller in that direction. In some cases, they are indicated as beingrelatively far from the target with only one light illuminated. As theuser moves the controller in that direction, more lights will illuminatein that quadrant, and then into the next two adjacent quadrants, thenortheast and southwest quadrants. As the user gets closer on center tothe port, the lights will continue to illuminate until the controller isdirectly centered. When it is centered, all of the lights willilluminate to confirm the controller is on target. A mark could then bemade on the skin to direct the user on where to target the needle, or aguide could be used to direct the syringe and needle towards the port.

FIG. 8 illustrates an exemplary tag data processing module 800 (such asmay be used for module 250 of locator 210 in FIG. 2). The processingmodule 800 takes the sum signals 802, 806 from the antenna array orsystem (e.g., from antenna system 500 of FIG. 5) and converts thesesignals to digital with converters 810, 816 and performs absolutemagnitude computation with element 820. A logic component 830 isprovided in module 800 to interpret the tag data, such as port, band, ortag model, type, and/or serial number and/or patient and treatment data.The interpreted/processed data from the tag response signal may bestored in tag data cache 840 and used by the controller and GUI 850 fordisplaying the data on the locator display (or on another device inwired or wireless communication with the locator). The GUI 850 may alsobe used to receive and process date input by an operator for writing tothe tag memory.

Transmission control element 860 may be used by the locatorcontroller/microprocessor to control transmission of interrogation/readsignals and/or write signals (e.g., signals to add or changediscretionary information such as a collar/band's previous and mostrecent inflation amount) 862 to the RFID tag. The transmit controlelement 860 also provides a transmission timing synchronization signal866 to the location processing module (such as module 240 or 700).During location processes or after the port is located, the locator(such as locator 200 in FIG. 1) is in some embodiments able to read andwrite information to the RFID tag of the port such as current device orpatient data, inputting physician's or technician's name, the date, andother useful data, with the handheld locator often operating to store orretain the port history/information in its own memory. The display ofthe locator, which may include visual and audio outputs, typically willdisplay or output the data being read and entered into the port RFID tagas well as providing location information and/or positioning guidance(as discussed above).

Although the invention has been described and illustrated with a certaindegree of particularity, it is understood that the present disclosurehas been made only by way of example, and that numerous changes in thecombination and arrangement of parts can be resorted to by those skilledin the art without departing from the spirit and scope of the invention,as hereinafter claimed. To practice the invention, the gastric bandsthat are adjusted by the internal band adjustment systems of theinvention may be external to the stomach as shown in FIG. 1, forexample, or may be provided or implanted internal to the stomach and/oresophagus, i.e., the gastric bands regulated according to the inventionmay be intragastric bands. Such an intragastric band may take the sameor similar form of the bands described with reference to FIG. 1 oranother form (such as forms described in the following incorporatedreference), and for example, may be attached and/or implanted in anumber of ways such as shown in U.S. Pat. Appl. Publ. No. 2005/0192601,which is incorporated herein by reference.

1. A gastric band system adapted for locating an access port,comprising: a gastric band with a fill line having an access port forreceiving a needle, wherein the access port comprises a radio frequencyidentification (RFID) tag; and a locator comprising: a radio frequencytransmitter generating an interrogation signal, wherein the RFID tagoperates in response to the transmitted interrogation signal to generatea tag response signal; an antenna array with an array face having aminimum of two pairs of antennae positioned an equal distance apart fromeach other, each of the antennae being spaced an equal distance from acentral axis of the antenna array, the array operable by the radiofrequency transmitter for transmitting the interrogation signal andreceiving the tag response signal; and a location processing moduleprocessing the tag response signal to determine location information forthe access port, wherein the location processing module processes adifference signal for each pair of antennae to determine the locationinformation for the access port, the difference signals being generatedbased on the tag response signal received by each of the antennae. 2.The system of claim 1, wherein the access port comprises a surface forreceiving the needle and the RFID tag comprises an antenna positioned atleast partially about the periphery of the receiving surface of the portand wherein the location information is indicative of substantiallybeing in the center of the receiving surface.
 3. The system of claim 1,wherein the location information comprises a signal strength value anddirection information relative to the array face from the locator. 4.The system of claim 3, wherein the locator further comprises a receiverprocessing module operating prior to the location processing module togenerate an in-phase tag response signal and a quadrature tag responsesignal from each of the difference signals.
 5. The system of claim 1,wherein the locator further comprises a tag data processing moduleprocessing a sum signal generated by the antenna array based on the tagresponse signal to obtain tag data stored in memory associated with theRFID tag.
 6. The system of claim 1, wherein the radio frequencytransmitter generates a write signal comprising patient treatment datafor transmittal to the RFID tag and wherein the RFID tag comprisesmemory and is operable in response to receiving the write signal tostore the patient treatment data in the memory.
 7. The system of claim1, wherein the locator comprises a display operable to display thelocation information and comprises a receptacle for receiving a syringewith a needle, the receptacle being configured to position the needleperpendicular to the array face and about at the center of the antennaarray.
 8. A locator apparatus for locating an implantable medicaldevices such as access ports of gastric bands, comprising: a transmittergenerating a read signal; an antenna array receiving a response signalfrom an identification tag mounted on an implantable medical device inresponse to the read signal, wherein the antenna array comprises fourantennae mounted on a planar mounting element in a diamond pattern witheach of the antennae being a predetermined distance from the center ofthe diamond pattern and wherein the antenna array generates a differencesignal for each opposing pair of the antennae based on the receivedresponse signal; and a location processing module processing thedifference signals to determine location information for the implantablemedical device relative to the antenna array.
 9. The apparatus of claim8, wherein the identification tag is an RFID tag and the transmitter isa radio frequency transmitter and the apparatus further comprising areceiver processing module operating to mix the difference signals witha sample of the transmitted read signal and to filter background noisefrom the mixed signals to generate in-phase tag response signals andquadrature tag response signals and wherein the location processingmodule processes the in-phase tag response signals and the quadraturetag response signals to determine the location information.
 10. Theapparatus of claim 9, wherein the determined location informationcomprises strength information for the response signal and directioninformation relative to the center of diamond pattern of the antennaarray.
 11. The apparatus of claim 8, further comprising a housing withinwhich the planar mounting element is mounted, wherein the housingcomprises a recessed surface for receiving a syringe, the recessedsurface including a needle guide passing through the housing adapted forreceiving a needle attached to the syringe, and wherein the needle guidepasses through the center of the diamond pattern of the antenna array.12. The apparatus of claim 8, wherein the antenna array further isconfigured to output a sum signal for each of the opposing pairs of theantennae and further comprising a tag data processing module processingthe sum signals to identify data stored in memory of the identificationtag provided in the tag response signal.
 13. A system adapted forlocating a port, comprising: an implantable medical device with a fillline having a port for receiving a needle, wherein the port comprises aradio frequency identification (RFID) tag; and a locator comprising: aradio frequency transmitter generating an interrogation signal, whereinthe RFID tag operates in response to the transmitted interrogationsignal to generate a tag response signal; an antenna array operable bythe radio frequency transmitter for transmitting the interrogationsignal and receiving the tag response signal, wherein the antenna arraycomprises a minimum of two pairs of antennae positioned an equaldistance apart from each other, each of the antennae being spaced anequal distance from a central axis of the antenna array; and a locationprocessing module processing the tag response signal to determinelocation information for the access port, wherein the locationprocessing module processes a difference signal for each pair ofantennae to determine the location information for the access port, thedifference signals being generated based on the tag response signalreceived by each of the antennae.
 14. The system of claim 13, whereinthe antenna array the location information comprises a signal strengthvalue and direction information relative to the array face.
 15. Thesystem of claim 14, wherein the locator further comprises a receiverprocessing module operating prior to the location processing module togenerate an in-phase tag response signal and a quadrature tag responsesignal from each of the difference signals.
 16. The system of claim 13,wherein the locator further comprises a tag data processing moduleprocessing a sum signal generated by the antenna array based on the tagresponse signal to obtain tag data stored in memory associated with theRFID tag.
 17. The system of claim 13, wherein the radio frequencytransmitter generates a write signal comprising patient treatment datafor transmittal to the RFID tag and wherein the RFID tag comprisesmemory and is operable in response to receiving the write signal tostore the patient treatment data in the memory.
 18. An access port forpositioning beneath the skin of a patient to provide access to a medicaldevice, comprising: an antenna for receiving an interrogation signalfrom a locator; memory storing port information; and circuitry forresponding to the received interrogation signal to generate a responsesignal comprising at least a portion of the stored port information,whereby the locator functions to determine location information for theaccess port, wherein the locator comprises an antenna array with anarray face having a minimum of two pairs of antennae used to transmitthe interrogation signal and receive the response signal, the antennaepositioned an equal distance apart from each other, each of the antennaebeing spaced an equal distance from a central axis of the antenna array,and further wherein the locator comprises a location processing module,wherein the location processing module processes a difference signal foreach pair of antennae to determine the location information for theaccess port, the difference signals being generated based on theresponse signal received by each of the antennae.
 19. The access port ofclaim 18, wherein the access port further comprises a body with asurface for receiving a needle, wherein the antenna, memory, andcircuitry are provided in a radio frequency identification (RFID) tagmounted on or within the body proximate to the needle receiving surface,and the interrogation signal is a radio frequency signal.
 20. The accessport of claim 18, wherein the access port comprises a surface forreceiving a needle and the antenna is positioned at least partiallyabout the periphery of the receiving surface of the port and wherein thelocation information is indicative of the locator being proximate to thereceiving surface of the port.
 21. The access port of claim 18, whereinthe memory further stores data pertaining to the patient that can bemodified by write signals from the locator and wherein the responsesignal further comprises the stored patient data.
 22. The access port ofclaim 18, wherein the location information comprises a signal strengthvalue and direction information relative to the array face from thelocator.